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          zookeeper
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        <h2 id="Watcher接口"><a href="#Watcher接口" class="headerlink" title="Watcher接口"></a>Watcher接口</h2><p>实现Watcher的类是一个回调函数，process中实现的方法，会在znode变更的时候触发</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">interface</span> <span class="title">Watcher</span>() </span>&#123;</span><br><span class="line"><span class="comment">// 不太懂为啥在Wacher中又定义了一个interface</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> interface <span class="title">Event</span><span class="params">()</span></span>&#123;        </span><br><span class="line">        <span class="keyword">public</span> <span class="class"><span class="keyword">enum</span> <span class="title">EventType</span></span>&#123;&#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">abstract</span> <span class="keyword">public</span> <span class="keyword">void</span> <span class="title">process</span><span class="params">(WatcherEvent event)</span></span>&#123;&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<a id="more"></a>
<p>调用zookeeper.create的时候要求传入权限控制参数（ACL），找了文章发现在UNIX中权限的管理还是很有意思的：<br><a href="http://ifeve.com/zookeeper-access-control-using-acls/">http://ifeve.com/zookeeper-access-control-using-acls/</a><br>有空可以继续研究一下</p>
<h2 id="继续看zookeeper"><a href="#继续看zookeeper" class="headerlink" title="继续看zookeeper"></a>继续看zookeeper</h2><p>发现在构造函数的实现中，有两个Thread。这个就有意思了，为啥在构造函数中有Thread？可以继续追踪下去 </p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">SendThread sendThread = <span class="keyword">new</span> SendThread(clientCnxnSocket); </span><br><span class="line">ReadThread eventThread = <span class="keyword">new</span> EventThread();</span><br></pre></td></tr></table></figure>
<p>查阅资料可以了解到zookeeper实现了一个事件驱动模型，先贴一张图或许有助于理解：</p>
<p><img src="https://static.oschina.net/uploads/img/201702/05224610_HZKB.gif" alt="来源http://www.wangjingfeng.com/38.html" title="在这里输入图片标题"></p>
<p>来源<a href="http://www.wangjingfeng.com/38.html">http://www.wangjingfeng.com/38.html</a></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">sendThread</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">void</span> <span class="title">run</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="comment">// 实现NIO</span></span><br><span class="line">        <span class="comment">// pendingQueue等待响应的packet，outgoingQueue等待发送的packet</span></span><br><span class="line">        <span class="comment">//int waitTimeOut, List&lt;Packet&gt; pendingQueue, LinkedList&lt;Packet&gt; outgoingQueue,ClientCnxn cnxn</span></span><br><span class="line">        clientCnxnSocket.doTransport(waitTimeOut, pendingQueue, outgoingQueue,cnxn)&#123;&#125;;</span><br><span class="line">    &#125;   </span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h3 id="EventThread-gt-BlockedQueue-gt-SendThead"><a href="#EventThread-gt-BlockedQueue-gt-SendThead" class="headerlink" title="EventThread -&gt; BlockedQueue -&gt; SendThead"></a>EventThread -&gt; BlockedQueue -&gt; SendThead</h3><p>通过加锁固定长度的队列实现消费者模型，同时sendThread使用了java自带的NIO技术，每次轮询所有的selector，处理已经传输完成的selector。很好的实现了解耦。</p>
<h2 id="一些其他class"><a href="#一些其他class" class="headerlink" title="一些其他class"></a>一些其他class</h2><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">ClientCnxn</span> </span>&#123;</span><br><span class="line">    <span class="comment">// ClientCnxn是一个管理I/O的类， 包含了一系列的可用的servers，并且控制这些servers的开关</span></span><br><span class="line">    </span><br><span class="line">&#125; </span><br></pre></td></tr></table></figure>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">AuthData</span> </span>&#123;</span><br><span class="line">    String scheme;</span><br><span class="line">    <span class="keyword">byte</span> data[];</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">static</span> <span class="class"><span class="keyword">class</span> <span class="title">Packet</span> </span>&#123;</span><br><span class="line">    RequestHeader requestHeader;</span><br><span class="line">    ReplyHeader replyHeader;</span><br><span class="line">    Record request;</span><br><span class="line">    Record response;</span><br><span class="line">    ByteBuffer bb;</span><br><span class="line">    AsyncCallBack cb;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">EventThread</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">void</span> <span class="title">queueEvent</span><span class="params">(WatcherEvent watcherEvent)</span></span>&#123;&#125;</span><br><span class="line">    <span class="function"><span class="keyword">void</span> <span class="title">queuePacket</span><span class="params">(Packet packet)</span></span>&#123;&#125;</span><br><span class="line">    <span class="function"><span class="keyword">void</span> <span class="title">processEvent</span><span class="params">(Object event)</span></span>&#123;</span><br><span class="line">        WatcherSetEventPair pair = (WatcherSetEventPair) event;</span><br><span class="line">        watcher = pair.watchers;</span><br><span class="line">        watcher.process(pair.event);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">ClientCnxnSocketNio</span></span>&#123;</span><br><span class="line">    </span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
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